The purpose of our studies is to elucidate cellular and biochemical mechanisms involved in "Neoplastic Development", using rat tracheal epithelial (RTE) cells transformed in culture by chemical carcinogens. In studies designed to define the growth and differentiation abnormalities of early transformants we found that the so called Enhanced Growth (EG) variant, has a markedly increased self renewal capacity, but nevertheless gives rise to a large number of terminally differentiating progeny. The cell composition of the EG variant clones changes or dramatically with time. At 5 weeks after exposure, only about 1% of the cells have clonogenic potential, while at 12 weeks such clones contain 10-30% colony forming cells. These changes in transformed stem cell pool sizes are accompanied by changes in responsiveness to physiologic regulators of growth (and differentiation) such as retinoids. Early transformants were growth inhibited by 10-9 M concentration of retinoic acid (RA), however with time their RA sensitivity decreased greater than 100-fold. Another aspect of our studies is concerned with elucidation of molecular mechanisms of RTE cell transformation. A number of neoplastically transformed RTE cell lines were analyzed for expression of oncogenes. The oncogenes N-myc, abl, fes, erbB and myb were not expressed and the genes myc, fos, raf and K-ras were expressed at levels similar to normal RTE cells. H-ras expression was increased in 3 of the tumor lines. Most interesting was the elevated expression (5-19-fold) of a c-fms related message in several of the cell lines. The message size detected was 9.5 kb. In comparison the fms message size in normal rat alveolar macrophages was about 4 kb. No evidence for gene amplification or rearrangement was found. Future studies will be aimed at identifying the ligand for this putative, fms-related growth factor receptor.